The present invention relates to a method and apparatus for treatment of biological tissues of a living body and more particularly to a medical apparatus and method for pulsed electric field treatment induced by a time varying magnetic field.
Heretofore there has been considerable activity in medical research into the use of direct current, alternating current and pulse signals of single and double polarity in the treatment of biological tissues of living bodies. These research activities have included invasive treatments that utilize implanted electrodes as well as non-invasive techniques utilizing capacitively or inductively coupled induced electric fields. That electric fields stimulate biological changes other than nerve action potentials or thermal effects, which effects occur at much higher field intensities, has previously been demonstrated by producing polarity-selective bone growth and resorption.
In accordance with the present invention, non-invasive techniques are utilized to induce a pulsed electric field in the presence of a concomitant magnetic field to stimulate tissue regeneration or resorption in ordered biological structures, such as bone, or to stimulate cellular chemistry modifications of non-ordered biological structures as found in blood or blood serum. The use of induced, rather than conducted, electric fields for stimulation of osteogenesis has been disclosed in the U.S. Pat. No. 3,893,462 issued to Michael P. Manning. Specific waveform induced electric field strength and pulse repetition patterns using a time varying magnetic field for the treatment of living tissue and/or cells has been disclosed in the U.S. Pat. No. 4,105,017 issued to John P. Ryaby. In accordance with the disclosure in each of these United States patents, the particular field patterns utilized have been shown to require treatment times of several hours per day extending over a period of months. Further, the coil currents required to achieve the stated induced electric fields with the waveforms disclosed in these patents require the use of heavy treatment coils to avoid excessive heating and the consumption of excessive amounts of power through dissipation of the magnetic field energy of the coils. This severely restricts the range of electric field strengths and waveform durations available for treatment and further inhibits the portability of the apparatus. Furthermore, the orientation of the magnetic field and the concomitant induced electric field is spatially fixed and therefore cannot provide symmetrical or uniform stimulation of the treated region. As a result, unwanted spurious growths are often observed after the successful treatment of the original fracture area.
A still further drawback of known techniques for noninvasive treatment utilizing induced electric fields is the potential hazard of electric shock inherent with the large energy storage in high voltage capacitors associated with the waveforms and levels of stimulation.
While it has been recognized and established through research and clinical evaluation that a change in an electrical and/or electromechanical environment of a living cell and/or tissue produces a therapeutic effect on growth, repair and maintenance behavior of the tissue and/or cell, there has not been a general acceptance of such techniques within the medical community. The invasive techniques which implanted electrodes had serious side effects that all but eliminated these techniques. Surgically noninvasive direct inductive coupling, on the other hand, has met with some success and is now being seriously considered by the medical profession. However, there still remains objections to the use of direct inductive coupling primarily for the reasons previously discussed, in particular, the power requirement, weight, and shock hazard. The present invention provides for noninvasive induced pulsed electric fields and conmitant magnetic fields that minimize these disadvantages as found in systems heretofore considered by the medical profession.